The disposal of non-merchantable debris which accumulates in the processing of logs, in a manner which is environmentally acceptable is becoming increasingly costly. The traditional incineration of the material in an open field fire is not satisfactory where residential townsites have developed in proximity to log yards. Burying is expensive and suitable burial site availability has been significantly reduced. Conventional incinerators require that the fuel size be small and uniform yet log yard waste is in sizes from small pieces up to full logs. The cost of reducing this waste material to usable fuel sizes has rendered the use of conventional incinerator types non-economic. Simple pit incinerators have been successful where dry ambient conditions result in a relatively moisture free debris.
Incineration of debris, particularly forest residue, requires a burner capable of receiving as fuel log sections as big as several feet in diameter and up to about thirty feet in length together with small branches and having a moisture content varying from a few percent to well over 100% and to burning this variable mixture at emission levels acceptable to a residential area.
Canadian Patent No. 1,013,619 issued July 12, 1977 to Weholt discloses a portable unit for burning debris. In this system an open top outwardly flaring combustion chamber having means for applying under fire air at the bottom of the chamber and air curtains across the outlet from the chamber formed by opposed interfacing jets at the top of the flaring side wall. These curtains are directed to intersect each other about midway across the chamber and inhibit the escape of material from the chamber before being completely combusted.
The intersecting air curtains utilized in this system produces counter rotating inter mixing currents within the chamber in the area of a second combustion zone (above the burning debris and immediately below the air curtain) in an attempt to ensure substantially complete combustion of debris within the combustion chamber.
U.S. Pat. No. 3,785,302 issued Jan. 15, 1974 to Davis corresponding Canadian patents 1,024,398 and 1,030,001) discloses a device similar to that described in the Weholt patent and includes means for providing both combustion air and supplementary fuel under pressure through the bottom wall and utilizes interfering air jets from the opposite side walls and directed into the chamber at different angles to form air curtains impeding movement of gases and other material from the combustion zone in a manner similar to the Weholt patent. In Davis the jets may be moveable or rotatable about a horizontal axis on the side walls to change the angle of impact of the air curtains.
Canadian Patent No. 1,080,038 issued June 24, 1980 to Applegate discloses a blower assembly for applying an overhead air curtain to a pit burner for burning debris. The pit is the combustion chamber and a portable blower applies an overhead air curtain that directs air from one side across the open top of the pit and deflected downward off the opposite wall into the pile of burning debris to provide all the combustion air for the debris.